"Please specify questionnaire ID.")); exit(); } else if(!mysqli_query($connection, "SELECT * FROM questionnair WHERE id = $id_questionnaire;")) { http_response_code(400); echo json_encode(array("error" => "Given questionnaire ID ($id_questionnaire) not in database.")); exit(); } $query = "SELECT * FROM `question` WHERE `id` IN (SELECT `id_question` FROM `questionnair_question` WHERE `id_questionnair`=".$id_questionnaire.");"; $result = mysqli_query($connection, $query); print ''; while($row = mysqli_fetch_assoc($result)) { print ''; } }